1. Field of the Invention
The present invention relates to a technique of a two-dimensional optical scanner and a light stimulus apparatus, and more particularly, to a technique of a two-dimensional optical scanner and a light stimulus apparatus including an acousto-optical deflector (AOD).
2. Description of the Related Art
Light stimulation means irradiation of a small region of a cell or a reagent with light such as a laser beam by using an optical device such as a microscope. The light stimulation is performed so as to observe or measure a reaction by the light irradiation.
A light stimulus apparatus includes a two-dimensional optical scanner so as to irradiate a desired position with light. In a general light stimulus apparatus for microscopes, a galvanomirror that controls an irradiated position by controlling the angle of a mirror is used as the two-dimensional optical scanner.
For example, the light stimulus apparatus is used in an experiment of stimulating nerve cells. In the experiment of stimulating nerve cells, a plurality of separate regions (nerve cells) need to be stimulated by switching the regions at high speed. However, it is difficult for the light stimulus apparatus including the galvanomirror to sufficiently meet such demands. In the galvanomirror, the angle of the mirror is continuously changed. Thus, normally, the irradiated position is also continuously moved. Therefore, it is difficult for the light stimulus apparatus including the galvanomirror to stimulate the plurality of separate regions without stimulating other regions by discontinuously changing the irradiated position.
In view of the above technical problem, a light stimulus apparatus including an acousto-optical deflector as the two-dimensional optical scanner instead of the galvanomirror has been proposed. The light stimulus apparatus including the acousto-optical deflector is disclosed in Japanese Patent Laid-Open No. 2008-26885, for example.
The acousto-optical deflector includes a crystal of tellurium dioxide or the like, and a transducer such as a piezoelectric element attached to the crystal. The transducer propagates an acoustic wave through the crystal, to thereby cause unevenness in the refractive index with respect to light. The acousto-optical deflector can thereby deflect incident light by acting as a diffraction grating with respect to the incident light. Also, since the deflection direction of emission light is changed depending on the frequency of a high-frequency signal applied to the transducer, the acousto-optical deflector can discontinuously change an irradiated position.
Accordingly, the light stimulus apparatus including the acousto-optical deflector can stimulate a plurality of separate regions by switching the regions at high speed.